The present invention relates to a fuel injection nozzle for use in a fuel injection valve in an internal combustion engine, etc.
A known integral type fuel injection nozzle described in Japanese Laid-Open Patent Publications Nos. 9-66381 and 9-126095 is shown in partial front sectional view in FIG. 1. The fuel injection nozzle 10 is molded from steel material and has a valve opening 13 in which a fuel injection valve 12 is slidably provided, a valve seat or seat portion 14, and a rounded or xe2x80x9csackxe2x80x9d portion 16, which has a generally semi-spherical inner circumferential surface 16a. An injection opening 17 is formed in the sack portion 16 and fuel is injected into the engine through this injection opening 17. The injection opening 17 is formed in the nozzle 10 by laser machining from the downstream side or the upstream side in the fuel injection direction.
However, if the injection opening 17 is formed from the downstream side using a laser machining process, dross accumulates in the fuel injection nozzle 10, and the measuring accuracy of injection fuel may be diminished. Dross is metal burrs that are formed when the metal melts during the laser machining process and adheres to the nozzle 10.
On the other hand, if the injection opening 17 is formed from the upstream side using a laser machining process, an optical fiber must be connected to a laser beam emitting apparatus and the laser machining process is indirectly performed by inserting the optical fiber into the valve opening 13. In this case, because the laser beam emitted by the optical fiber scatters, a special beam condensing device must be utilized to condense the laser beam. Furthermore, because the valve opening 13 is generally small (approximately 6 mm) in diameter, the machining accuracy of the opening profile is limited.
An electric spark machining process also can form an injection port. However, because the time required to fabricate the injection port using an electric spark machining port is substantially longer than the time required for laser machining, manufacturing efficiency is reduced.
A known two-piece type fuel injection nozzle described in Japanese Laid-Open Patent Publication No. 6-249105 is shown by partial sectional view in FIG. 2. This fuel injection nozzle 20 comprises a valve seat 21 made from steel material and a nozzle tip 25 molded from ceramic. A valve opening 23, in which a fuel injection valve 22 is slidably secured, and a seat portion 24, on which the valve 22 contacts, are formed on the valve seat 21. The nozzle tip 25 includes a sack portion 26 having a generally semi-spherical inner circumferential surface 26a and an injection opening 27. The valve seat 21 and nozzle tip 25 are joined by a brazing material 29 using a brazing process. However, because brazing these two parts is difficult, manufacturing costs are relatively high.
It is, accordingly, an object of the invention to provide improved fuel injection nozzles that can be manufactured efficiently.
In one aspect of the present teachings, improved manufacturing processes are described that facilitate the joining of the valve seat and the nozzle tip of a fuel injection nozzle.
In another aspect of the present teachings, improved methods for forming an injection opening in the nozzle tip are described.
In a further aspect of the present teachings, improved methods for manufacturing a fuel injection nozzle are described in which an optionally shaped injection opening having excellent measuring accuracy can be easily formed on the nozzle tip in a short time.
Other objects, features and advantages of the present invention will be readily understood after reading the following detailed description together with the accompanying drawings and the claims.